Parliamentary Voting System and Constituencies Bill

Could I raise almost the opposite point of view? Many people who are in prison are already registered to vote at their home address. What is to stop them using the postal vote system to cast their vote, even though they are in prison? All it requires is for them to apply for it from that home address. The postal vote arrives at their home. Some relative takes it in to them, they cast their vote, the relative takes it back, puts it in the post and they have voted. Or are we going to use prison records as part of the access data?